Hitherto, gel materials are extensively used for articles of food, medical products, living goods, industrial products and the like. Although a variety of kinds of polymer compounds are used for these, only two kinds of physical gel and chemical gel exist from the viewpoint of structure.
Physical gel is a gel usually seen in natural world, such as gelatin or agar-agar. Additionally, a greater part of the tissue of a living body is occupied with a variety of physical gels.
Such physical gel constitutes a network under a physical attraction acted between polymers, and therefore it is low in stability against temperature and solvent.
To the contrary, chemical gel is a huge single molecule in which direct bondings with covalent bonds are made in the whole network, and therefore it is excellent in stability against temperature and solvent so as to be industrially used in various fields.
However, in chemical gel, a crosslinking point is fixed, and therefore an inhomogeneous structure formed by a crosslinking reaction is permanently kept so that it has the defect of being remarkably low in mechanical strength.
Against this, in recent years, a proposition with a new method has been made for a new kind of gel, namely, “slide-ring gel or topological gel” which cannot be classified into either physical gel or chemical gel. Polyrotaxane is used for such slide-ring gel.
In this polyrotaxane, a linear molecule (axis) includes a cyclic molecule (rotator) in such a manner as to pierce through the opening of the cyclic molecule, and blocking groups are placed at both end terminals of the linear molecule to prevent the cyclic molecule from leaving from the linear molecule. A crosslinked polyrotaxane applicable to the slide-ring gel is disclosed (see patent literature 1), in which a plurality of such polyrotaxanes are crosslinked with each other.
Patent literature 1: Japanese Patent No. 3475252 publication
In this crosslinked polyrotaxane, the cyclic molecule pierced with the linear molecule is movable along the liner molecule (by a pulley effect) so that the crosslinked polyrotaxane has a viscoelesticity. Accordingly, if a tension is applied to the crosslinked polyrotaxane, the tension is uniformly dispersed under this pulley effect, and therefore it has the excellent characteristics of being difficult to cause crack or flaw, differently from a conventional crosslinked polymer.